Method for coating a thin,uniform thickness stripe on a substrate



Dec. 29, 1970 M A c s ETAL 3,551,201

METHOD FOR COATING A THIN, UNIFORM THICKNESS STRIPE ON A SUBSTRATI Original Filed Jan. 13. 1967 2 Sheets -Sheet 1 MICHAEL A. MARCHESE LEWIS G. TAFT Dec. 29, 1970 STRIPE ON A Original Filed Jan. 13, 1967 WW /W 17 NIFO TRAT M. AQMARCHESE E AL METHOD FOR COATING A THIN, U

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United States Patent 3,551,201 METHOD FOR COATING A THIN, UNIFORM THICKNESS STRIPE ON A SUBSTRATE Michael A. Marchese, Boulder, 'Colo., and Lewis G. Taft, San Jose, Calif., assignors to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Original application Jan. 13, 1967, Ser. No. 609,171, new Patent No. 3,461,841, dated Aug. 19, 1969. Divided and this application Mar. 4, 1969, Ser. No. 804,227 Int. Cl. H01f 10/00; B05c 1/16 U.S. Cl. 117-235 3 Claims ABSTRACT OF THE DISCLOSURE A stripe of varying cross-section is deposited from a die onto a moving substrate and subsequently dried into a hardened structure of uniform thickness.

BACKGROUND OF THE INVENTION This application is a division of U.S. patent application S.N. 609,171, filed Ian. 13, 1967, now U.S. Pat. 3,461,841.

FIELD OF THE INVENTION The present invention has application to the general field of extruding fluid material through an extrusion die and onto a continuously moving flexible substrate to form a final, dried, flat stripe of material having a uniform cross-section. The invention has particular application to the field of applying magnetic recording material to a substrate and since good magnetic recording head to recording media contact is required for a good recording performance, the stripe, when hardened, must have both uniform thickness and a flat contact head surface.

DESCRIPTION OF THE PRIOR ART Magnetic sound tracksin stripe form have been applied to films or like substrates in the past by various coating apparatus. One prior art apparatus is characterized by a uniform rectilinear die opening, known as a flat die, under which circumstances the dry coating, rather than having a flat and uniform cross-section, is characterized by the presence of a valley or recess in the center of the stripe which greatly inhibits the subsequent magnetic recording of information.

In an attempt to obtain a more uniform deposit of magnetic sound tracks on moving substrates, the mag netic stripe material also has been laid' down directly from a nozzle rather than by the use of an extrusion die, in which case the nozzle is provided with a cross-sectional shape other than rectilinear to prevent the entrapping of air as the material is being applied to the substrate.

In the type of apparatus where the liquid to be stripped passes through an extrusion die onto the moving substrate, attempts have been made to supply a greater mass of material at the center point of the deposit and to utilize the pre-application of spaced edge strips of the same material to induce the rapid flow of the material from the center to the edges and thereby affect a uniform cross sectional thickness. In the general coating field, it is also A Patented Dec. 29, 1970 ice the time of deposit at the center of the stripe is purely happenstance. In the second type of apparatus, the employment of prestriping the edges to define the stripe area in an attempt to induce resultant uniform thickness to the stripe greatly complicates the coating procedure. In the third form of apparatus, where en mass coating of the substrate is achieved by first dipping and then selective removal of the stripe material, it is hard to closely control the width of the stripe deposit.

SUMMARY OF THE INVENTION The present invention is directed to the method of die extrusion of magnetic material in stripe form onto a moving substrate including a reservoir for supplying the stripe material to the die. The die opening is substantially rectilinear and has an arcuate upper face to ensure the controlled extrusion of magnetic material of initial maximum thickness at the center of the stripe, whereby, upon subsequent drying, the stripe is characterized by a flat surface of uniform cross-section. The crowned die of the present invention advantageously consists of a central, adjustable die member movable vertically between spaced guide members. Adjustment of the center, curved section of the crown die assembly varies the thickness of the stripe while maintaining uniform cross-sectional thickness of the dried stripe. The employment of an upper concave, horizontal extrusion surface which constitutes an arc of a circle of a given radius ensures uniformity in variance of an initial thickness of the stripe deposit. The radius of curvature may be readily varied depending upon the viscosity of the material being coated, and the width of the stripe being applied.

A BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view, partially in section, of a preferred form of the improved die extrusion apparatus of the present invention for depositing a flat magnetic stripe onto a moving substrate.

FIG. 2 is a side elevation, in section, taken about'lines 22 of the apparatus shown in FIG. 1.

FIG. 3 is an elevation, in section, of a portion of the apparatus shown in FIG. 2 taken about lines 3-3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is shown the improved die extrusion apparatus of the present invention, which is particularly applicable to coating a thin stripe of magnetic recording material on a substrate, which moves at relatively high speed through the apparatus. Magnetic material (not shown) in fluid form is maintained at a given level within hopper 10 which is mounted in front of and above an extrusion die formed of metal and indicated generally at 12. The hopper 10' includes spaced side walls 14, a vertical rear wall 16, and an inclined front wall 18 to define a hopper bottom outlet 20. A reciprocating valve member of like configuration in the form of a plunger 22 is shown in closed position preventing magnetic stripe material from passing downwardly through nozzle 24. The valve plunger 22 is supported by means (not shown) and movement of valve stem 26 upwardly, unseats valve 22, allowing the magnetic material within the hopper 10 to pass downwardly through the lower nozzle opening 28 onto moving substrate 30 (shown in dotted line form). Substrate 30 passes longitudinally through the apparatus in the direction indicated by arrow (FIG. 2). The hopper 10 is fixedly supported on a base or table member 34, including lower and upper sections 36 and 38, respectively. The lower base member 36 is recessed at 37 and cooperates with recess 40 carried by the upper table section 38 to define a longitudinally extending cavity 42. Further, the upper table section 38 is centrally recessed at 44 to receive adjustable extrusion die assembly 12. In this respect, the extrusion die assembly cooperates with a vertically adjustable support block 46. Block 46 is fluid biased by a pair of spaced fluid motors 48 and 50 (indicated in dotted lines, FIG. 1). The fluid motors form a part of block member 52 which is positioned within the lower part of the working cavity 42. The fluid motors include, respectively, vertically adjustable pistons 54 and 56, having their upper ends rigidly coupled to the bottom of the support block 46 at spaced points. The support block 46 moves upwardly in response to the application of a biasing fluid to the fluid motors through a common fluid inlet 57. The block member 46 moves upwardly to a point defined by the thickness of the substrate member 30 and the position of die assembly 12. The transversely extending pin 58 carried within block 52 limits the movement of the support block 40 to the vertical direction under the influence of the fluid motors 48 and 50.

A pair of bracket members 60 hold vertical support blocks 62 and transversely extending support block 64 at the rear of the apparatus. The blocks 62 and 64 form the support assembly for the vertically adjustable extrusion die assembly 12. In this respect, the transverse support block 64 is bored centrally at 66 to fixedly receive an internally bored and threaded, flanged sleeve member 68. The sleeve member 68 receives a threaded bolt 70 which is also threadably received within upper die carrier 72. The die assembly 12 further includes opposed, spaced guide members 74 and 76, which may be fixedly coupled both to support member 62 and to the upper table section 38 within recess 44. With the guide members 74 and 76 fixed to the stationary support members, the guide members define a narrow passageway for the moving elements of the die assembly 12. The upper movable die carrier 72 is coupled to a lower movable die carrier 78 by means of a pair of pins 80. The lower movable die carrier 78 holds, as an element thereof, a generally rectangular die element 82 including a concave bottom surface 84.

The concave surface 84 forming the crowned die, in cross-section, is defined by an arc of a circle of a given radius. The lower face 84 of the die cooperates with a pair of spaced carbide guide rails 86 and 88 to define in conjunction with the substrate surface a generally rectilinear die opening 90 having a uniform and closely controlled height varying from the center of the die opening outwardly, to accurately control the deposit of coating material onto the substrate 30 as it moves through the apparatus. Adjusting screws 92 are carried by the fixed main guide members 74 and 76, to fix the carbide guide rails within recesses 93 formed within respective main guide members 74 and 76. It is noted in FIG. 3 that there is a slight vertical gap at 94 between the bottom of the guide rails 86 and 88 and the top surface of substrate 30. In actual practice, this gap disappears upon the application of fluid pressure to fluid motors 48 and 50 which causes the support block 46 to move upwardly. This also prevents the escape of fluid magnetic recording material from the die area except in an axial or forward direction. The stripe deposit has a cross-sectional configuration of like form to that presented by guide rails 86 and 88 and the crowned die member 82. It is further noted that suitable, elongated slots 96 in die carriers 78 and 98 in die carrier 72 allows the die assembly, including sections 72, 78 and 80, to be adjusted vertically regardless of the transversely extending screw members 100, 102 and 104, which join the main guide sections 74 and 76 together at points spaced vertically of the assembly.

The die extrusion apparatus, in the vicinity Where the substrate makes its entry to the working area, is provided with curved or relieved surfaces so that the substrate, as it enters, does not come into abrupt contact with the support block or pressure pad 46. In this respect, the front edge 106 of the block member 46 (FIG. 2) is rounded or curved. Likewise, at the front of the machine, the back dam member 108 fixed to the upper table section 38 is further provided with a curved or tapered front edge 110 for the same purposes. Theback darn 108 does not extend rearwardly to the extent of the movable die assembly 12, but terminates to form an area 112, above the substrate which receives fluid magnetic material. The side walls of the extrusion apparatus are so machined that the material to be extruded can pass only through the opening defined by the guide members 86, 88, crowned die 82 and the substrate. Where the substrate is exiting from the extrusion apparatus, at end 114, the edges 116 of the support block or pressure pad 46 are kept sharp as is the bottom rear edge 118 of the extrusion die member 82. This is important in order to achieve the exact dimensions of the stripe which otherwise might be lost if the substrate were deflected in the area of the crowned die.

The to be striped substrate 30 is urged against the die by the support block 46. The pressure pad or support block 46 comes into physical contact with the area exactly beneath the carbide rails 86 and 88 so that a discrete stripe of accurate width may be formed.

In order to ensure that the proper position of the weblike substrate 30 as it passes through the apparatus, an adjustable guide member, carried by block 52, cooperates with a fixed guide member on the opposite side of the crown die. A spring-biased adjustable guide 120, rectangular in cross-section, is positioned on the top of the block member 52 with its position being vertically determined by screw member 122. The coil 124 tends to bias the block to the right such that a rectangular recess 126 formed on the right-hand face receives the left-hand edge of the moving substrate web 30 (FIG. 2). The right-hand edge of the same substrate is merely abutted against the outer edge fixed guide block 128 which is coupled to the bottom face of the upper table member 38 by a suitable mounting screw 130.

The concave surface 84 forming the crown die is defined as an arc of a circle of a given radius. Depending upon the width of the stripe being applied to the substrate and the viscosity of the material being coated, greater or lesser curvature is given to the adjustable die element. For coating a fiat stripe of from one fourth of an inch to one half of an inch in width of a specific composition having a viscosity in the order of 1000 c.p.s. to about 6000 c.p.s., a crown die having a radius of curvature in the order of to inches is quite adequate to ensure, after drying, the formation of a stripe of uniform crosssectional thickness. If a narrow stripe is desired, in the order of an eighth of an inch, a radius of curvature for the crown die in the order of about 60 inches will provide the desired results, assuming, of course, that the viscosity of material being applied remains the same. If widths of up to about one inch are desired, the curvature of the arched upper face of the die opening may be the arc of a circle of on the order of about 200 inches. Further, in the use of the above described apparatus with a magnetic material composition, the speed of coating may be varied within the range of 30 feet per minute to about 200 feet per minute.

The desired curvature to the crown die is necessitated by rheological or flow properties of the viscous fluid through the die. These flow properties are similar to laminar flow, such as any viscous material experiences as it flows near a solid boundary. Thus, a narrower stripe requires a greater amount of curvature to allow more of the ink in the center portion where there will be a substantially more rapid flow than in a wider stripe. Conversely, where a wider stripe is desired, there would be less of a variation of flow in the center portion of the stripe and thus, would require less additional ink to fill it out. While the preferred material was used at a viscosity of from 2,000 to 5,000 c.p.s., viscosities of up to about 10,000 c.p.s. can be utilized with appropriate modification of the die and radius of the crown of the die.

With the die extrusion apparatus of the present invention, the crown die is slidably mounted between the carbide guide rails on each side. This allows for the vertical adjustment of the die as desired. The height of the crown die above the substrate is determined substantially by the height of the carbide rails at their point of contact with the lowest portion of the crown die. This height is calibrated with a tenth indicator (not shown) from the fiat surface of the carbide rail, which will come in contact with the substrate to the lowest corner of the crown die. Obviously, only one rail need be calibrated as the two side rails are parallel, being mounted so within the recesses of the stationary die elements 74 and 76. The preferred height of the die is four to five mils which results in a stripe, approximately .5 mil thickness being deposited.

The overall apparatus forms one element in the production of magnetic recording media. An oven (not shown) is turned on and the fans within it start to bring the oven up to a desired drying temperature for the stripe after it is coated. The web which, for instance, may constitute Mylar polyester, is started moving through the apparatus at a predetermined speed, such as 100 feet per minute. The plunger element 22 of the apparatus is lifted. This allows the magnetic ink (not shown) to flow out of the hopper container down into the crown and die section entering area 112. After the flow of ink has started, a bank of ink builds up within the carbide rails between the front portion of the crown die 82 and the back dam 108. After this initial build-up of the ink, which is almost instantaneous, the composition flows out or escapes through the die opening 90 in the desired stripe configuration onto the substrate 30. A continuing supply of ink allows a continuous stripe to be formed. After the substrate is coated, the magnetic particles may be oriented by an external magnetic field, the oriented media then passing into a preheated drying oven where the solvent is removed by evaporation. After drying, the substrate may be readily wound onto a reel for additional processing, as desired.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that 6 various changes in formand details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of forming a fiat stripe of coating material on a substrate, comprising the steps of:

passing said substrate beneath a die, causing liquid coating material whose viscosity is on the order of 1000 cps. to about 10,000 cps. and constituting solid coating material in a solvent to issue in a single application from said die onto the surface of said substrate in the form of a stripe having a convex upper surface;

and removing the solvent fromsaid liquid coating material by evaporation to dry said material into a hardened structure having a uniform cross-section and a flat upper surface.

2. A method of depositing a flat stripe of coating material on a substrate as claimed in claim 1, wherein said coating material is issued from the die having a concave upper surface opposite said substrate.

3. A method of depositing a fiat stripe of coating material on a substrate as claimed in claim 1, wherein said coating material has magnetic properties.

References Cited UNITED STATES PATENTS 2,357,992 9/1944 Banghart 118415 2,748,016 5/1956 Speed et al 118415X 2,779,307 1/1957 Foresta et al 118413 3,203,393 8/1965 Colwill et a1. 118413X 2,573,097 10/1951 Epstein 118253X 2,879,176 3/1959 Franck et a1 1l7-235 3,023,123 2/1962 Colwill et al. 117-235 WILLIAM D. MARTIN, Primary Examiner B. D. PIANALTO, Assistant Examiner U.S. Cl. X.R. 

